1. Field of the Invention
The present invention relates to a substrate of a liquid crystal display device (LCD), and a method for manufacturing the same. In particular, the present invention relates to a method for manufacturing a substrate of a liquid crystal display wherein an organic layer and a pixel electrode thereon are firmly cohering to each other.
2. Description of Related Art
A conventional substrate of a liquid crystal display device having a switching element and a pixel electrode is formed, mentioned as follows, referring to FIGS. 1a and 1b. FIGS. 1a and 1b show the inverse staggered structure of the thin film transistor (TFT).
Referring to FIG. 1a, a gate electrode 60a is formed on a transparent substrate 10. A gate insulation layer 50 is deposited thereon to cover the gate electrode 60. A semiconductor layer 90 with an island shape is formed on the gate insulation layer 50 on the gate electrode 60. On the surface of the semiconductor layer 90, ohmic contact layers 92a and 92b are formed in separate regions. On one ohmic contact layer 92a, a source electrode 70a is formed and a data line 70 connecting to the source electrode 70a is formed on the gate insulation layer 50. On the other ohmic contact layer 92b, a drain electrode 70b is formed. As the gate electrode, source electrode and the drain electrode are formed, a TFT acting as a switching element is completed.
On the substrate having the TFT, an organic layer 55, including a benzocyclobutene (or BCB) generally containing combinations of C, H and O elements, is formed. A contact hole 30 is formed to expose some surface of the drain electrode 70b by patterning the organic layer 55. The reason for using the organic layer on the substrate of the LCD is that after being coated on the substrate of which surface has stepped profile, the surface of the organic layer does not project the stepped profile. That is, a substantially flat surface of the organic layer is formed. Also, the organic layer has a lower coefficient constant similar to the inorganic layer, such as silicon oxide (SiOx) or silicon nitride (SiNx). Therefore, after the organic layer is formed on the substrate, a pixel electrode can be formed over the area on which the data line is formed in order to maximize the aperture ratio. In that regard, an ITO (Indium Tin Oxide) layer is deposited on the organic layer having the contact hole 30 and is patterned to form a pixel electrode 40 by etching the ITO layer with the photo-resist 88 pattern using a wet etching method. It is possible to overlap the pixel electrode and some portion of the data line because problems such as cross talk do not occur between them due to the characteristics of the organic material mentioned above.
However, during the etching process, the ITO layer can be easily peeled off from the organic layer or a vacancy can occur between the ITO layer and the organic layer because the coherency between them is very weak. As a result, the etchant can penetrate into the vacancy so that the pixel electrode can be over etched, as shown in FIG. 1b. FIG. 1b shows the undesirable patterned results which (A) is the peeled off portion of the pixel electrode (B) and (C) are the over etched portion of the pixel electrode.
If the edge portions of the ITO layer, which constitutes the pixel electrode, are over etched by the etchant, then the size of the pixel electrode is reduced and becomes irregular. This is referred to as a CD loss. As a result, the aperture ratio becomes smaller than the expected value.
In order to overcome the above-mentioned problem, an object of the present invention is to suggest a method for manufacturing a substrate of the LCD in which the coherence between the pixel electrode and the organic layer is enhanced as well as the structure of the LCD by the same method. Another object is to protect the pixel electrode from being over etched by enhancing the coherence of the pixel electrode with the organic layer.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The present invention suggests a method in which an intermediate thin layer 156 is formed by treating the surface of the organic layer 155 with plasma of H2, as shown in FIG. 2a. The organic layer typically comprises C, H, and O radicals. As a result, the surface of the organic layer has an unstable state. The present invention suggests an enhanced method for making the surface of the organic passivation layer more stable by treating it with plasma containing H element. Consequently, the pixel electrode fabricated on the treated region has stronger adherence and maintains its shape and size. When the surface of the organic layer is treated with the H2 plasma, the surface has an Oxe2x80x94H bonding structure. Therefore, as an ITO layer or a metal layer is deposited thereon, the coherence of it on the organic layer is enhanced. As a result, it is possible to protect the inorganic layer, such as an ITO layer or an metal layer deposited on the organic layer, from being peeling off and being undesirably patterned.
According to this scope, the present invention suggests an LCD comprising a substrate, a TFT on the substrate, an organic layer covering the TFT, an intermediate layer 180, as shown in FIG. 2b is formed by treating the surface of the organic layer with H2 plasma, a contact hole exposing a surface of a drain electrode of the TFT by removing some portion of the organic layer and the intermediate layer, a pixel electrode connecting to the drain electrode through the contact hole. The present invention also suggests an LCD according to the above-mentioned structure wherein the intermediate layer is further formed on the side wall of the contact hole.
Additionally, the present invention suggests a method for manufacturing an LCD comprising steps of forming a TFT on a substrate, forming an organic layer covering the TFT, treating the surface of the organic layer with H2 plasma, forming a contact hole exposing some surface of the drain electrode by removing some of the organic layer and intermediate layer, forming a pixel electrode connecting to the drain electrode through the contact hole. The present invention also suggests a method for manufacturing an LCD according to the above-mentioned method wherein the step of forming a contact hole is performed after forming the organic layer, and then the step of treating the surface of the organic layer is performed so that the side wall of the contact hole also has the intermediate layer on the surface.
These and other aspects, features and advantages of the present invention will be better understood by studying the detailed description in conjunction with the drawings and the accompanying claims.